Drop custom implementation of EVENTLET_HUB
Drop custom implementation of EVENTLET_HUB

Eventlet uses monotonic clocks by default since 0.21, hence no need
to patch that anymore.

Closes-Bug: #1906262
Co-Authored-By: Dimitri John Ledkov <446b8b5d376e3ab2e6b2d5d0d93dc2d3de728b2c@ubuntu.com>
Co-Authored-By: Michael Hudson-Doyle <5e87ffb38a52af6fb9a19b679e9122c7a4d601a5@ubuntu.com>
Change-Id: I72106068d99cc174412aa3026082ec63f1d895fe

openstack/oslo.service